The present invention relates to an improvement in copying apparatus for the transport of an image support member with an unfused electrically disturbable image thereon.
In a transfer electrostatographic process such as conventional transfer xerography, in which an image pattern of dry particulate unfused toner material is electrostatically transferred to a final image support surface (the copy sheet) from an initial image support surface (the charged photoreceptor surface developed with toner), the transferred toner is typically only loosely adhered to the final support surface and is easily mechanically and electrically disturbed by the subsequent necessary process of stripping the final support surface away from the initial support surface and transporting it to a toner fuser. The copy sheets themselves are thin, relatively delicate and may be highly variable in condition, humidity, material, weight, etc..
In xerography, the toner image transfer is most commonly achieved by electrostatic force fields created by D.C. charges applied to or adjacent the back of the copy sheet while the front side of the copy sheet contacts the toner bearing photoreceptor surface. These transfer fields must be sufficient to overcome the forces holding the toner onto the photoreceptor and to attract a substantial portion of the toner onto the copy sheet. The transfer fields are generally provided in one or two well known ways; by ion emission of D.C. charges, from a transfer corona generator, deposited onto the back of the copy paper, or by a D.C. biased transfer roller or belt rolling along the back of the paper, and holding it against the photoreceptor. In either case the copy sheet must be held in registration with, and moved together with, the imaging surface in order to transfer a registered and unsmeared image. Particularly in the conventional transfer accomplished by D.C. corona charges applied to the back of the copy sheet, these transfer charges also provide a substantial "tacking" force which electrostatically holds the copy sheet down against the imaging surface for the movement of the copy sheet therewith. This electrostatic transfer charge typically remains, in part, on the copy sheet after it is stripped.
The present invention is particularly suitable for a stripped copy sheet vacuum transport system of the type disclosed in U.S. Pat. No. 4,017,065, issued Apr. 12, 1977, to R. Poehlein, and U.S. Pat. No. 3,578,859, issued May 18, 1971, to W. K. Stillings.
Accordingly, the present specification is based on, and incorporates by reference under MPEP S608.01(p) p. 48.3, the specification of said U.S. Pat. No. 4,017,065 as a part of this specification.
Desirably included in the present system is a detacking corotron taught in U.S. Pat. No. 3,870,515, issued Mar. 11, 1975, to Norbett H. Kaupp as well as in the above-cited Poehlein patent. This system utilizes a detacking or transfer charge neutralizing corona generator to remove most of the tacking charge. However, it is not desirable to remove all of the transfer charge on the copy sheet to aid in stripping, since that may also reduce the electrostatic retention of the toner image to the copy sheet.
The Poehlein patent incorporated herein describes the vacuum manifold sheet guide system shown in the present drawings forming a part of the stripping system after stripping of the lead edge has been initiated and providing the transport of the unfused toner image bearing copy sheets.
The present invention is directed to the solution of a particular problem in the transportation of the copying member bearing the unfused and electrically disturbable image thereon. Toner disturbances have been noted which are apparently due to air ionization between the copy sheet and its post-stripping vacuum manifold transport, after it has been stripped from the photoreceptor. This breakdown is believed to occur from sharp edges or discontinuities in the conductive copy guide manifold, particularly at its downstream end where the copy sheet departs from this conductive paper guide. These electrical toner disturbances can seriously undesirably affect the image before it can be fused, under certain conditions.
The present disclosed system provides an opposing electrically biased or grounded conductive baffle closely spaced from the conductive surface of the vacuum manifold in the areas where toner disturbances have been a problem. As shown in the embodiment herein, in the paper path after the copy sheet has been stripped from the photoreceptor, and before the toner is fused, the copy sheet is transported between two closely spaced conductive surfaces. This second conductive surface or baffle is preferably smoothly curved away from the vacuum manifold at the downstream end of the vacuum manifold.